The invention relates to mixers having closed cylindrical mixing chambers and rotors for mixing material therein. Specifically, the invention relates to a mixer having a rotor with internal passageways for the material undergoing mixing. The material is squeezed through the rotor when the rotor is both rotated and moved axially back and forth in the mixing chamber.
Mixers having rotors with internal passageways to aid in mixing have been known for more than ten years, for example U.S. Pat. No. 3,623,703 to Nielander issued Nov. 30, 1971. Such mixers have the advantage that as the simultaneous rotation and axial movement of the rotor is underway, string-like portions of the material to be mixed are continually sheared off from the mass of the material and are forceably mixed in both the radial and the axial directions. Very high shearing forces for shearing gradients are obtained. Such mixers are well suited for both mixing and plastication operations. Because the material to be mixed or plasticated is also pressed against the internal rotor surfaces defining the passageways, very high friction forces are also obtained. Such friction forces are particularly important in mixing and plastification, even on the molecular level.
Not only flowable or plastic material can be processed with such a mixer but also powdery, granular or solid materials with or without the presence of other flowable or plastic material. Regarding specific types of materials to be mixed, thermoplastic materials are plasticated to the required extent during the mixing and plasticating process. If additive materials are inorganic or non-thermoplastic materials, they are preferably reduced in size such as by grinding and dispersed to the required extent during the mixing and plasticating process. It is also possible to mix plastics, rubber, or other highly viscous or liquid materials very effectively with powdery or granular fillers, pigments, dye-stuffs and other chemical additives, e.g. raw rubber with carbon black and other additives.
In spite of the inherent advantages in the basic concept of the mixer having a rotor with internal passageways, such mixers have not become widely used because of inherent disadvantages present with prior art mixers of this type. One disadvantage is the particularly difficult problem of cleaning the internal passageways of the rotor. Prior to using the rotor for another type of material or after processing the last batch at the end of a work day, the rotor has to be cleaned.
Prior cleaning methods are cumbersome and involve cleaning one rotor passageway at a time with a hand tool. Manual cleaning requires great effort because the processed material tends to cure or vulcanize while still on rotor parts. In doing such manual cleaning work there is always the danger of the rotor getting damaged or of the worker getting injured when a tool slips. Also, in cleaning one passageway at a time, the material in the last passageway has more time to solidify or to vulcanize than the material cleaned out of the first passageway. Even if the cleaning work is relatively effortless at the beginning, it becomes more difficult with time.
Not only the rotor passageways must be cleaned but also other surfaces on the rotor and the mixing cylinder. With time, the mixed material may vulcanize on these parts as well and present difficult cleaning problems. Vulcanized material is generally less soluble in solvents than uncured material. It is thus desirable to clean the plastic material while it is still uncured. For these reasons, the worker having the task of cleaning the rotor and other associated apparatus is always under time pressure which itself increases the danger of damage or accidents.
Accordingly, it is a primary object of the present invention to provide an apparatus for cleaning a rotor having internal passageways, the apparatus providing rapid cleaning and requiring little manual work.
Another advantage of the present invention is the provision of a mechanical cleaning apparatus which cleans all rotor internal passageways simultaneously.
Another advantage of the present invention is the provision of a mechanical cleaning apparatus for the internal passageways in a rotor which does not damage the rotor.
Another advantage of the present invention is the provision of a mechanical cleaning apparatus for the internal passageways of a rotor allowing rapid cleaning of the rotor and other parts of the mixing apparatus before the processed material has time to cure.